The present invention relates to an image display apparatus to be employed in a television set or a computer peripheral display and a method of making the same.
Cathode ray tubes have been mainly used as the image display apparatus for color television sets. Since cathode ray tubes have a large depth as compared to the size of the screen, it has been difficult to make a flat type television set.
EL (electro-luminescent) devices, plasma displays and liquid crystal display devices have been used for flat type image display devices. However, these devices have not provided satisfactory performance for luminance, contrast, and color reproducibility.
A conventional flat type screen device is shown in FIG. 7. The conventional device includes an image which is to be projected onto a fluorescent screen and which is first divided into vertical sections vertically having a number of lines. Each image is also divided into horizontal subsections. The horizontal and vertical subsections are arranged in a matrix so that when the image is displayed there is not a gap between subsections.
Electron beams are deflected and scanned on the screen within each subsection. The electron beams cause red fluorescent material, green fluorescent material, and blue fluorescent material on the screen to emit colored light. A color image signal controls the amount of electrons with the electron beam to produce the image. The emitted color light from each subsection forms the entire image on the fluorescent screen. The construction of the conventional image display apparatus is explained below.
FIG. 7 is an internal perspective view of a conventional image display apparatus. The image display apparatus includes a rear electrode 101, a linear cathode 102a, 102b and 102c which are used to generate electrons, extraction electrode 103, focusing electrode 105, horizontal deflection electrode 106, and vertical deflection electrodes 107a and 107b.
These components are disposed in a front container 108 and rear container 109 which hold the components in a vacuum.
Rear electrode 101 is a flat conductive sheet disposed in parallel with the linear cathodes 102a, 102b, and 102c. Linear cathodes 102a, 102b, and 102c are parallel to each other and formed in the vertical direction from top to bottom. Each linear cathode 102a, 102b, and 102c extends along the horizontal (Y axis) direction to produce an electron flow having a nearly uniform current-density-distribution in the horizontal (X axis) direction traveling from the back of the display to the front of the display. Although three linear cathodes 102a, 102b, 102c are shown in the figure, there may be more linear cathodes. Linear cathodes 102a, 102b, and 102c are made of a tungsten wire coated with an oxide.
Extraction electrode 103 is a conductive sheet 111 formed substantially parallel to rear electrode 101 having linear cathodes 102a, 102b, and 102c disposed between the extraction electrode and the rear electrode. Holes 110 are formed in extraction electrode 103 and aligned in the horizontal (Y axis) direction at regular intervals to correspond to each linear cathode 102a, 102b, 102c.
Electrons are generated by linear cathodes 102a, 102b, and 102c and formed into a predetermined number of separate electron beams by passing through holes 110 in extraction electrode 103. Although holes 110 are shown as circular, other shapes for holes 110, such as ellipse, rectangular, or slit-shaped, may be used.
Signal electrode 104 is formed of oblong strips 112. Oblong strips 110 extend from the bottom to the top of the apparatus in the vertical (Z axis) direction and are aligned in the horizontal (Y axis) direction at predetermined intervals. Holes 113 are formed in each of the strips 112 along the Z axis at locations corresponding to holes 110 in extraction electrode 113. In response to an image signal provided to signal electrode 104, signal electrode 104 controls the electron beam's passing through holes 113. Holes 113 may be shaped differently such as an ellipse, rectangular, or slit.
Focusing electrode 105 is a conductive sheet 115 having apertures 114. The holes 114 correspond to strips 112 of signal electrode 104 in the Z axis direction. Focusing electrode 105 controls the intensity of the electron beam. Holes 114 may be shaped as an ellipse, rectangular, or slit.
Horizontal deflection electrode 106 is formed of pairs of conductive strips. Each pair includes strips 116a and 116b which extend along the vertical (Z axis) direction in parallel to each other. The strips 116a and 116b are formed on either side of holes 114 of focusing electrode 105.
Vertical deflection electrode 107 has a pair of comb-shaped conductive sheets 107a and 107b which are interdigitated with each other in the horizontal direction along the same plane.
A fluorescent material layer which emits light when irradiated by an electron beam is coated over an inner surface of the front container 108 forming screen 119. A metal-back layer (not shown) is attached to screen 119.
Extraction electrode 103, signal electrode 104, focusing electrode 105, horizontal deflection electrode 106 and vertical deflection electrode 107 form electrode unit 122. Each electrode is joined by an insulating binder (not shown). Electron beam 117 emitted from line cathode 102 passes through holes 110, 113, and 114 of extraction electrode 103, signal electrode 104, and focusing electrode 105 respectively, and through horizontal deflection electrode 106 and vertical deflection electrode 107 prior to reaching screen 119.
Each electrode of the conventional apparatus must be manufactured and assembled with high accuracy to obtain an uniform image without borders on the fluorescent screen.
In operation, line cathodes 102 are heated by a heater current so that electrons are easily emitted. While the line cathodes 102 are heated, a voltage is applied to rear electrode 101, line cathode 102, and extraction electrode 103.
Line cathodes 102 emit a sheet shaped electron beam. Holes 111 of extraction electrode 103 divide the sheet shaped electron beam into separate electron beams. Then, the electron beams arrive at holes 113 of signal electrode 104. Signal electrode 104 controls the amount of electrons in each electron beam which passes through holes 113 in response to a video signal which is provided to signal electrode 104.
After passing through signal electrode 104, the electron beams are focused at the focusing electrode 105. The electron beams are focused and shaped by an electrostatic-lens-effect caused by apertures 114. The electron beams are deflected horizontally and vertically by providing a potential difference between the adjacent conductive sheets 116a and 116b of horizontal deflection electrode 106, and holes 118a and 118b of vertical deflection electrode 107.
Finally, the electron beams are accelerated to a high energy level by a high voltage which is applied to the metal-back layer of screen 119. The high energy electron beams collide with the metal-back layer causing light to be emitted from the fluorescent material layer.
The screen is horizontally and vertically divided into a matrix arrangement including subsections 120 and 121. Each subsection 120 and 121 is scanned by deflecting one electron beam corresponding to the separated electron beams separated using extraction electrode 103. Accordingly, an entire image is displayed on the screen including red, green and blue video signals which correspond to respective picture elements. The picture elements are continuously controlled by the voltage applied to signal electrode 104.
However, to achieve a quality image, it is required that the electrodes be produced with great position and positioned with high accuracy to obtain a picture with good uniformity without any noticeable border lines between subsections 120 and 121 on screen 119.
As shown in FIG. 8, vertical electrode 107 includes two conductive sheets 107a and 107b. The two conductive sheets 107a and 107b are joined. The conductive sheets 107a and 107b are also joined to horizontal deflection electrode 106 by insulating binder 126 shown in FIG. 9B.
Horizontal deflection electrode 106 and vertical deflection electrode 107 are joined in a high temperature electric furnace. Horizontal deflection electrode 107 is very thin and narrow having a depth of 0.2 mm and a width of 3.6 mm. As the image display apparatus is enlarged, the length of the electrode plates become large. For example, a diagonal six-inch image display apparatus has corresponding conductive sheets of 130 mm in length. Because of the increased length, when conductive sheets 107a, 107b and horizontal deflection electrode 106 are joined in the high temperature electric furnace, deformation in conductive sheets 107a and 107b may result as shown in FIG. 9A. The deformation causes an unsuitable deflection of the electron beam. This results because the deflection is determined by the potential difference between conductive sheets 107a and 107b. If the conductive sheets are deformed, an uniform picture will not be produced. In addition, conductive sheets 107a and 107b may not be positioned along the same plane which causes a difference in the level between conductive sheets 107a and 107b.
The improper deflection of the electron beams 123 and 124 as a result of the defective vertical electrode 107 is shown in FIG. 10. The difference in level between conductive sheets 107a and 107b causes the electron beams to imprecisely strike a subsection of screen 119. Fluctuation in the electron beams striking each subsection on screen 119 prevents a highly uniform picture from being produced.
As is evident from the forgoing, a flat type image display apparatus which has a high quality image and avoids the above problems is needed.